Range for loop for statements

[Alvov1]

Closes #181

Adds a nested RowIterator class to Statement that enables range-based for loops over query results:

SQLite::Statement query(db, "SELECT id, name FROM test");
for (SQLite::Statement& row : query)
{
    std::cout << row.getColumn(0).getInt() << "\n";
}

Notes:

• begin() calls reset() automatically, so re-iterating the same Statement always starts from the beginning
• Bindings set before the loop are preserved across reset()
• Empty result sets are handled correctly (loop body never executes)
• RowIterator satisfies std::input_iterator_tag with full iterator traits

[SRombauts]

The PR description calls this "full iterator traits." The traits are all here, but the interface isn't: there's no operator== and no post-increment operator++(int) next to this operator!=. Range-based for only calls operator!=, so nothing breaks today. The catch is that anyone who reaches for it with <algorithm>, or checks it against the C++20 std::input_iterator concept (which requires ==), hits a wall. Either add operator== and post-increment, or soften the claim to "usable in range-based for loops."

[SRombauts]

This line is redundant: the copy constructor gets generated anyway. Declaring it also has two quiet side effects: it makes implicit copy-assignment deprecated, and it suppresses the implicit move members, so moves fall back to copy (harmless for a single pointer, but not the intent). The RowIterator() = default; above it is the one that's actually needed, since the Statement* constructor suppresses the implicit default constructor. For a trivial pointer holder I'd drop this line and let copy, move, assignment, and the destructor stay implicit (Rule of Zero). Not blocking.

[SRombauts]

Very minor and not blocking, not really an issue: the diff drops a blank line here (and another around prepareStatement() below) that aren't part of the iterator change. You could revert them to keep the diff focused, but it's completely fine to leave as-is if you prefer.